Heretofore, various types of rich-lean combustion burners have been proposed. With a view to accomplishing NOx reductions, it is arranged that a lean-side mixture whose air ratio (the ratio of the amount of air to the amount of fuel) is in excess of 1.0 is burned at lean-side flame holes while on the other hand, with a view to accomplishing combustion-flame stability, it is arranged that rich-side flame holes, at which a rich-side mixture whose air ratio falls below 1.0 is burned, are arranged adjacent to the lean-side flame holes. For example, there is proposed in Patent Literature Publication 1 a rich-lean combustion burner comprising a row of lean-side flame holes which extends in the front-back direction (i.e., in the longitudinal direction) and a pair of rows of rich-side flame holes which extend in the front-back direction on both horizontal sides (both lateral sides), with the lean-side flame hole row interposed between the two rich-side flame hole rows. And, in such a rich-lean combustion burner, it is proposed that a common inlet port for supplying of rich-side mixture to the rich-side flame hole rows and an inlet port for supplying of lean-side mixture to the lean-side flame hole row are provided separately from each other.
Additionally, there has been a proposal to construct a rich-lean combustion burner whose entire shape is flat by joining or welding together thin plate members formed into their predetermined shapes by stamping process or other like shape forming process. For example, in Patent Literature Publication 2, it is proposed to form a rich-lean combustion burner comprising a row of lean-side flame holes which is sandwiched, from its both sides, between two rows of rich-side flame holes by multiple folding of a single sheet of thin material, whereby to accomplish work improvements in cutting process to be performed on individual members as well as in joining/welding process to be performed on the individual members.